An earmould is a piece of plastic or other soft material which is moulded to fit in the outer part of your ear and deliver the sound from a behind-the-ear hearing aid.  A hole (or ‘bore’) is drilled through the earmould roughly following the path of your ear canal.  The hearing aid is then connected to this bore using a short piece of clear, flexible tubing.  
Traditionally, earmoulds are made using transparent materials; however some hearing aid providers can provide coloured or decorative earmoulds.
It's extremely important to have earmoulds that fit well and are comfortable to wear. Poorly fitted earmoulds can cause feedback, soreness and discomfort, and can even impact on the effectiveness of the hearing aid.